Myotis grisescens - A.H. Howell, 1909
Gray Myotis
Other English Common Names: Gray Bat
Taxonomic Status: Accepted
Related ITIS Name(s): Myotis grisescens A. H. Howell, 1909 (TSN 179997)
Unique Identifier: ELEMENT_GLOBAL.2.104746
Element Code: AMACC01040
Informal Taxonomy: Animals, Vertebrates - Mammals - Bats
 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Mammalia Chiroptera Vespertilionidae Myotis
Genus Size: D - Medium to large genus (21+ species)
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Concept Reference
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Concept Reference: Wilson, D. E., and D. M. Reeder (editors). 1993. Mammal species of the world: a taxonomic and geographic reference. Second edition. Smithsonian Institution Press, Washington, DC. xviii + 1206 pp. Available online at: http://www.nmnh.si.edu/msw/.
Concept Reference Code: B93WIL01NAUS
Name Used in Concept Reference: Myotis grisescens
Taxonomic Comments: Monotypic (Decher and Choate 1995).
Conservation Status
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NatureServe Status

Global Status: G4
Global Status Last Reviewed: 23Mar2015
Global Status Last Changed: 23Mar2015
Ranking Methodology Used: Ranked by calculator
Rounded Global Status: G4 - Apparently Secure
Reasons: Essentially restricted to the cave region of the eastern and central United States; many occupied caves (hundreds) exist, and population size is large (a few million), but relatively few caves hold most of the population; total population and number of occupied caves increased in recent decades, due to ongoing cave protection efforts, but some occupied caves remain vulnerable to disturbance. Despite large population size and good recovery, the species is regarded as vulnerable to potential massive mortality from white-nose syndrome (no significant impact was known as of early 2015). The conservation status and rank should be reviewed in the near future as more information becomes available on the impact of white-nose syndrome on this species.
Nation: United States
National Status: N3N4 (02Jun2014)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Alabama (S2), Arkansas (S2S3), Florida (S1), Georgia (S1), Illinois (S1), Indiana (S1), Kansas (S1B), Kentucky (S2), Missouri (S3), North Carolina (S1), Oklahoma (S2), South Carolina (S1), Tennessee (S2), Virginia (S1)

Other Statuses

U.S. Endangered Species Act (USESA): LE: Listed endangered (28Apr1976)
U.S. Fish & Wildlife Service Lead Region: R3 - North Central
IUCN Red List Category: NT - Near threatened

NatureServe Global Conservation Status Factors

Range Extent: 200,000-2,500,000 square km (about 80,000-1,000,000 square miles)
Range Extent Comments: The range extends from southeastern Kansas and central Oklahoma east to western Virginia and western North Carolina, and from Missouri, Illinois, and Indiana south to southern Alabama and northern Florida (Decher and Choate 1995).The primary range is concentrated in the cave regions of Alabama, Arkansas, Kentucky, Missouri and Tennessee, with smaller populations found in adjacent states, including a growing population in a quarry in Clark County, Indiana (USFWS 2009). Summer and winter ranges are essentially the same.

Area of Occupancy: 6-25 4-km2 grid cells
Area of Occupancy Comments: Based on the area occupied by the vast majority of the hibernating population, the area of occupancy in winter is small (fewer than 20 grid cells measuring 2 km x 2 km). 

Number of Occurrences:  
Number of Occurrences Comments: The number of distinct occurrences (subpopulations) has not been determined using standardized criteria. Martin (2007) listed the species as occurring in 384 caves scattered across 11 states (his analysis did not include Indiana). Summering populations of gray bats use multiple caves, and movement between caves is considerable (Tuttle 1976a, Martin 2007).

Population Size: >1,000,000 individuals
Population Size Comments: Accurate population data is difficult to obtain, due to problems inherent with using various census techniques, complications associated with differences in observers' counting abilities, movements of bats between transient and permanent hibernacula or maternity sites, seasonality (e.g., counts at maternity sites before or after birth of young), inability to census all sites during the same year, and the potential of disturbing hibernating bats at critical hibernacula (USFWS 2009). Total population was estimated at 1.5 million in the early 1980s, approximately 3.4 million in 2005-2007 (Harvey and Currie 2007, Martin 2007).

Viability/Integrity Comments: Fewer than 20 caves contain the vast majority of the hibernating population (Harvey and Currie 2007, Martin 2007). Fern Cave in Alabama contains a large proportion, including over 1 million hibernating individuals (USFWS, news release, 8 April 2013). Ten caves each harbor greater than 100,000 hibernating individuals; 3 others each have more than 10,000 (Martin 2007).

Overall Threat Impact: High - medium
Overall Threat Impact Comments: Decline began with cave disturbance associated with saltpeter production during the Civil War. Some of the largest colonies were lost as a result of cave commercialization. Some caves were improperly gated.

Cave disturbance was the major factor in the historical decline. Cave protection efforts have greatly reduced this threat. However, human disturbance is the main reason for the continued decline of gray bats in caves that are not protected (USFWS 2009). The species is especially vulnerable due to its high fidelity to particular favored caves, and it is very sensitive to disturbance, including the mere presence of humans with lights; disturbance may result in bats moving to less favorable roosting places.

White-nose syndrome (WNS) recently was detected in this species. This emerging disease potentially could cause large, rapid declines. As of early 2015, no significant impact of the disease had been observed.

The use of forestry insecticides and crop pesticides in areas adjacent to riparian corridors where gray bats forage may reduce the prey base or kill bats that ingest contaminated insects (Northern Prairie Wildlife Research Center). Pesticide contamination (e.g., Clawson and Clark 1989, Clawson 1991) remains a concern but currently is not known to be causing declines (USFWS 2009).

Other threats include deforestation and impoundment of waterways (and subsequent cave inundation). Natural and human-caused flooding remains a secondary threat at some gray bat sites (USFWS 2009).

This species is not known to incur significant mortality from turbines at wind energy facilities (Arnett and Baerwald 2013).

Climate change could have a significant impact on gray bats. It is projected that a rise in ambient temperature could make traditional and currently occupied hibernacula and maternity sites unsuitable for roosting gray bats and cause a shift in the species' range northward. This could adversely affect the species' food supply, or affect the ability of bats to adequately deposit important fat reserves that are critical for winter survival (USFWS 2009). However, no documentation of such effects currently exists (USFWS 2009).

Short-term Trend: Increase of >10%
Short-term Trend Comments: Abundance has been relatively stable or increasing over the past 10 years or three generations. Of the 29 Priority 1 maternity sites listed in the 1982 approved Gray Bat Recovery Plan, an analysis of data received from state personnel throughout the range of the species and reports by Martin (2007), Sasse et al. (2007) and Elliott (2008) revealed that populations at 13 sites (45 percent) have been stable or increasing (USFWS 2009). Roughly 33 percent of Priority 2 caves across the species' range have stable or increasing populations; however, the applied time frame (five years) is believed to be insufficient for assessing population trends for this species (Sasse et al. 2007, USFWS 2009).

Long-term Trend: Decline of 10-50%
Long-term Trend Comments: Area of occupancy, number of subpopulations/locations, and abundance likely have decreased over the past 200 years, but the degree of decline is uncertain.

Area of occupancy, number of subpopulations/locations, and abundance have increased over the past several decades. Wide population fluctuations of gray bat numbers have been documented at many maternity sites, but there have been significant population increases in some of the major hibernacula (USFWS 2009).

The range has expanded in some areas (e.g., Georgia, Indiana, and Kansas), and gray bats are using many caves that were not known prior to the completion of the 1982 Recovery Plan. Martin (2007) reported nearly 500,000 gray bats at 8 hibernacula, where historically there had only been about 25,000 recorded.

Based on 1,879 observations of gray bats obtained from 334 roost locations (103 summer colonies and 12 hibernacula) in 14 states, Ellison et al. (2003) determined that 94 percent of the populations showed stable or increasing populations whereas 6 percent of populations decreased. Stable or increasing populations were reported for 83 percent of the 12 hibernating colonies examined.

Sasse et al. (2007) analyzed data from 48 gray bat maternity sites involving three subpopulations in Missouri, Arkansas, and Oklahoma between 1978 and 2002; 79 percent of the colonies were stable or increasing. Elliott (2008) examined population trends at nine Priority 1 caves and concluded that although the species had increased by approximately 21 percent between 1980 and 2005, it had reached only about 37 percent of its maximum historic populations at these sites.

Martin (2007) noted that gray bat population levels have increased approximately 104 percent since 1982.

According to USFWS (2009), Michael Harvey reported that the species increased from approximately 1,575,000 to roughly 2,678,000 in 2002 and to around 3,400,000 in 2004 (Ellison et al. 2003; Martin 2007).

Other NatureServe Conservation Status Information

Protection Needs: Occupied caves should be protected from human disturbance.

A buffer of undisturbed vegetation should be left around the entrances of caves inhabited by gray bats; wooded travel corridors between roosting and foraging sites should be protected; the use of herbicides and pesticides in areas adjacent to foraging and roost sites should be carefully controlled and monitored for unanticipated adverse effects (Alabama Forestry Commission).

Distribution
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Global Range: (200,000-2,500,000 square km (about 80,000-1,000,000 square miles)) The range extends from southeastern Kansas and central Oklahoma east to western Virginia and western North Carolina, and from Missouri, Illinois, and Indiana south to southern Alabama and northern Florida (Decher and Choate 1995).The primary range is concentrated in the cave regions of Alabama, Arkansas, Kentucky, Missouri and Tennessee, with smaller populations found in adjacent states, including a growing population in a quarry in Clark County, Indiana (USFWS 2009). Summer and winter ranges are essentially the same.

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
Endemism: endemic to a single nation

U.S. & Canada State/Province Distribution
United States AL, AR, FL, GA, IL, IN, KS, KY, MO, NC, OK, SC, TN, VA

Range Map
Note: Range depicted for New World only. The scale of the maps may cause narrow coastal ranges or ranges on small islands not to appear. Not all vagrant or small disjunct occurrences are depicted. For migratory birds, some individuals occur outside of the passage migrant range depicted. For information on how to obtain shapefiles of species ranges see our Species Mapping pages at www.natureserve.org/conservation-tools/data-maps-tools.

Range Map Compilers: Sechrest, 2002


U.S. Distribution by County Help
State County Name (FIPS Code)
AL Colbert (01033), Conecuh (01035), DeKalb (01049), Franklin (01059), Jackson (01071), Lauderdale (01077), Lawrence (01079), Limestone (01083), Madison (01089), Marshall (01095), Morgan (01103), Shelby (01117)
AR Baxter (05005), Benton (05007), Boone (05009), Carroll (05015), Franklin (05047), Independence (05063), Izard (05065), Johnson (05071), Lawrence (05075), Madison (05087), Marion (05089), Newton (05101), Pope (05115), Searcy (05129), Sharp (05135), Stone (05137), Van Buren (05141)
FL Baker (12003)*, Jackson (12063)
GA Bartow (13015), Carroll (13045), Catoosa (13047), Chattooga (13055), Cherokee (13057), Clarke (13059)*, Dade (13083), Gordon (13129), Murray (13213), Pickens (13227), Polk (13233)*, Walker (13295)
IL Adams (17001)*, Alexander (17003)*, Gallatin (17059), Hardin (17069), Jackson (17077), Jersey (17083), Johnson (17087), La Salle (17099), Monroe (17133), Pike (17149)*, Pope (17151), Pulaski (17153)
IN Clark (18019), Crawford (18025), Floyd (18043), Harrison (18061), Jennings (18079)*, Lawrence (18093)*, Perry (18123), Spencer (18147)
KS Crawford (20037)
KY Adair (21001), Allen (21003), Anderson (21005), Barren (21009), Bell (21013), Breckinridge (21027), Bullitt (21029)*, Butler (21031), Caldwell (21033), Calloway (21035), Carter (21043), Christian (21047), Clark (21049), Clay (21051), Clinton (21053), Crittenden (21055), Cumberland (21057), Daviess (21059), Edmonson (21061), Elliott (21063)*, Floyd (21071), Franklin (21073), Garrard (21079), Grayson (21085), Green (21087), Greenup (21089), Hardin (21093), Harlan (21095), Hart (21099), Henderson (21101), Hopkins (21107), Jefferson (21111), Jessamine (21113), Laurel (21125), Lee (21129), Livingston (21139), Logan (21141), Lyon (21143), Madison (21151), Meade (21163), Menifee (21165), Mercer (21167), Metcalfe (21169), Monroe (21171), Muhlenberg (21177), Nelson (21179), Ohio (21183), Oldham (21185), Owsley (21189), Perry (21193), Pulaski (21199), Scott (21209), Shelby (21211), Simpson (21213), Spencer (21215), Taylor (21217), Todd (21219), Trigg (21221), Trimble (21223), Union (21225)*, Warren (21227), Wayne (21231)*, Webster (21233)*, Whitley (21235), Wolfe (21237)
MO Audrain (29007), Barry (29009), Benton (29015), Boone (29019), Callaway (29027), Camden (29029), Carter (29035), Cedar (29039), Chariton (29041), Christian (29043), Cole (29051), Crawford (29055), Dade (29057), Dallas (29059), Dent (29065), Douglas (29067), Franklin (29071), Gasconade (29073), Greene (29077), Henry (29083)*, Hickory (29085), Howard (29089), Howell (29091), Iron (29093), Jasper (29097), Jefferson (29099), Laclede (29105), Lawrence (29109), Madison (29123), Maries (29125), Marion (29127), McDonald (29119), Miller (29131), Moniteau (29135), Morgan (29141), Newton (29145), Oregon (29149), Osage (29151), Ozark (29153), Perry (29157), Phelps (29161), Pike (29163), Pulaski (29169), Ralls (29173), Reynolds (29179), Ripley (29181), Shannon (29203), St. Clair (29185), St. Louis (29189), Ste. Genevieve (29186), Stone (29209), Taney (29213), Texas (29215), Washington (29221), Wayne (29223), Webster (29225), Wright (29229)
NC Buncombe (37021), Haywood (37087), Madison (37115), Swain (37173), Transylvania (37175), Yancey (37199)
OK Adair (40001), Cherokee (40021), Delaware (40041), Ottawa (40115), Sequoyah (40135)
TN Anderson (47001), Bedford (47003), Benton (47005)*, Bledsoe (47007)*, Campbell (47013), Cannon (47015)*, Carter (47019), Cheatham (47021)*, Claiborne (47025), Clay (47027), Cocke (47029), Coffee (47031), DeKalb (47041), Decatur (47039), Fentress (47049), Franklin (47051), Giles (47055), Grainger (47057), Greene (47059), Grundy (47061), Hancock (47067), Hardeman (47069)*, Hardin (47071), Hawkins (47073), Hickman (47081), Houston (47083)*, Jackson (47087), Jefferson (47089)*, Knox (47093), Lawrence (47099)*, Lewis (47101), Lincoln (47103), Marion (47115), Maury (47119), Meigs (47121), Montgomery (47125), Moore (47127), Overton (47133), Perry (47135), Putnam (47141), Rhea (47143), Roane (47145), Robertson (47147), Rutherford (47149), Sequatchie (47153), Smith (47159), Stewart (47161), Sullivan (47163), Sumner (47165)*, Unicoi (47171), Union (47173), Van Buren (47175), Warren (47177), Wayne (47181), White (47185), Wilson (47189)
VA Bristol (City) (51520), Lee (51105), Russell (51167), Scott (51169), Wythe (51197)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
03 Upper Oconee (03070101)+*, St. Marys (03070204)+*, Apalachicola (03130011)+, Chipola (03130012)+, Sepulga (03140303)+, Conasauga (03150101)+, Coosawattee (03150102)+, Oostanaula (03150103)+, Etowah (03150104)+, Upper Coosa (03150105)+, Middle Coosa (03150106)+, Upper Tallapoosa (03150108)+, Cahaba (03150202)+, Sipsey Fork (03160110)+
05 Upper New (05050001)+, Lower Levisa (05070203)+, Little Scioto-Tygarts (05090103)+, Little Sandy (05090104)+*, North Fork Kentucky (05100201)+, South Fork Kentucky (05100203)+, Upper Kentucky (05100204)+, Lower Kentucky (05100205)+, Upper Green (05110001)+, Barren (05110002)+, Middle Green (05110003)+, Rough (05110004)+, Pond (05110006)+, Muscatatuck (05120207)+*, Lower East Fork White (05120208)+*, Upper Cumberland (05130101)+, Rockcastle (05130102)+, Upper Cumberland-Lake Cumberland (05130103)+, Obey (05130105)+, Upper Cumberland-Cordell Hull (05130106)+, Collins (05130107)+, Caney (05130108)+, Lower Cumberland-Old Hickory Lake (05130201)+, Stones (05130203)+, Lower Cumberland (05130205)+, Red (05130206)+, Silver-Little Kentucky (05140101)+, Salt (05140102)+, Rolling Fork (05140103)+, Blue-Sinking (05140104)+, Lower Ohio-Little Pigeon (05140201)+, Highland-Pigeon (05140202)+, Lower Ohio-Bay (05140203)+, Saline (05140204)+, Tradewater (05140205)+, Lower Ohio (05140206)+
06 South Fork Holston (06010102)+, Watauga (06010103)+, Holston (06010104)+, Upper French Broad (06010105)+, Pigeon (06010106)+, Nolichucky (06010108)+, Watts Bar Lake (06010201)+, Lower Little Tennessee (06010204)+, Upper Clinch (06010205)+, Powell (06010206)+, Lower Clinch (06010207)+, Middle Tennessee-Chickamauga (06020001)+, Sequatchie (06020004)+, Guntersville Lake (06030001)+, Wheeler Lake (06030002)+, Upper Elk (06030003)+, Lower Elk (06030004)+, Pickwick Lake (06030005)+, Bear (06030006)+, Lower Tennessee-Beech (06040001)+, Upper Duck (06040002)+, Lower Duck (06040003)+, Buffalo (06040004)+, Kentucky Lake (06040005)+
07 The Sny (07110004)+, South Fork Salt (07110006)+, Salt (07110007)+, Peruque-Piasa (07110009)+, Lower Illinois-Senachwine Lake (07130001)+, Lower Illinois (07130011)+*, Cahokia-Joachim (07140101)+, Meramec (07140102)+, Bourbeuse (07140103)+, Big (07140104)+, Upper Mississippi-Cape Girardeau (07140105)+, Big Muddy (07140106)+, Cache (07140108)+, Lower Kaskaskia (07140204)+
08 Lower Hatchie (08010208)+*, Upper St. Francis (08020202)+
10 Little Chariton (10280203)+, Harry S. Missouri (10290105)+, Sac (10290106)+, Pomme De Terre (10290107)+, South Grand (10290108)+*, Lake of the Ozarks (10290109)+, Niangua (10290110)+, Lower Osage (10290111)+, Upper Gasconade (10290201)+, Big Piney (10290202)+, Lower Gasconade (10290203)+, Lower Missouri-Moreau (10300102)+, Lower Missouri (10300200)+
11 Beaver Reservoir (11010001)+, James (11010002)+, Bull Shoals Lake (11010003)+, Middle White (11010004)+, Buffalo (11010005)+, North Fork White (11010006)+, Upper Black (11010007)+, Current (11010008)+, Lower Black (11010009)+, Spring (11010010)+, Eleven Point (11010011)+, Strawberry (11010012)+, Little Red (11010014)+, Lake O' the Cherokees (11070206)+, Spring (11070207)+, Elk (11070208)+, Lower Neosho (11070209)+, Illinois (11110103)+, Robert S. Kerr Reservoir (11110104)+, Frog-Mulberry (11110201)+, Dardanelle Reservoir (11110202)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A small bat.
General Description: A bat with unicolored dorsal fur (gray after the mid-summer molt, at other times sometimes chestnut brown or russet); paler below, with hairs darker basally; wing membrane (gray) connects to the foot at the ankle; calcar is unkeeled; total length 80-105 mm; forearm length 40-46 mm; ear length 14-16 mm; tail length 33-45 mm; hind foot 9-12 mm; mass 7-16 g (usually 8-10 g). wingspread 275-300. Distinct sagittal crest on skull. Teeth 38; dentition I 2/3, C 1/1, P 3/3, M 3/3 (Barbour and Davis 1969, Sealander 1979).
Diagnostic Characteristics: Most likely to be confused with M. lucifugus, M. sodalis, M. austroriparius, and M. septentrionalis. Distinguished from these by uniform-colored dorsal fur from base to tip (all others have contrasting shades, bi- or tri-colored dorsal fur) and by attachment of wing membrane at ankle, not at base of toe (Barbour and Davis 1969, Tuttle 1978).
Reproduction Comments: Mating occurs in September-October. Adult females store sperm through the winter and become pregnant soon after emergence from hibernation (Gutherie and Jeffers 1938, Harvey 1994, Tuttle and Kennedy 2005)). One young is born late in May or in early June (reported as mid-June for Oklahoma; flying as early as late June or early July). In Florida, young are weaned in mid-July (Layne 1978). Larger colonies are more successful in raising young. Most young are able to fly in 20-35 days, depending on colony size. Individual females typically do not produce young until their second year. Recorded maximum longevity approximately 14-17 years but may be longer (Harvey 1992, Tuttle and Kennedy 2005). Maternity colonies include from a few hundred to many thousands of individuals.

Tuttle (1975) showed that growth rates of non-volant young are positively correlated with colony size, probably because increasing numbers of bats clustering together reduce the thermoregulatory cost per individual (Herreid 1963, 1967). In larger colonies, most young begin to fly from 20 to 25 days after birth, while in smaller colonies, or where colonies have been reduced due to disturbance, this time is increased to 30 to 35 days (Tuttle 1976). In severely reduced colonies, the young sometimes die before achieving flight (Tuttle in Brady et al. 1982). For newly volant young, growth rates and survival are inversely proportional to the distance from their roost to the nearest over-water foraging habitat (Tuttle 1976). Although mothers continue to nurse young for a period after the young are flying, juveniles are apparently left to learn how to hunt on their own (Tuttle and Stevenson).

Ecology Comments: Forage in loose groups, but become territorial when insect numbers decrease; territories seem to be controlled by reproductively-active females (Tuttle et al.).

Elder and Gunier (1981) determined that the mean annual survival rate is about 70% in males and 73% in females. Stevenson and Tuttle (1981) found that the after-first-year survival rate is about 55 to 85% in relatively undisturbed colonies, and 57 to 66% in disturbed colonies. Mortality is especially high in spring migration when fat reserves and food supply are low (Tuttle and Stevenson 1977).

Habitat Type: Terrestrial
Non-Migrant: Y
Locally Migrant: Y
Long Distance Migrant: Y
Mobility and Migration Comments: Wintering caves often are hundreds of kilometers from summer range. Individuals regularly migrate 17-437 kilometers between summer maternity sites and winter hibernacula, with some individuals moving as much as 689-775 kilometers (Hall and Wilson 1966, Tuttle 1976; Tuttle and Kennedy 2005). In some areas the same caves are used in winter and summer; in other areas (e.g., Missouri, Arkansas) many caves used in summer are vacant in winter. Most Florida breeders migrate north to hibernate in cooler caves of northern Alabama and central Tennessee; migration occurs mostly in September-October, some as late as November or December (Layne 1978), females preceding males. Females depart wintering caves in late March and early April, males in late April and May. Evidence suggests that bats migrate in small flocks (Barbour and Davis 1969). Small caves may be used as rest stops (Smith and Parmalee 1954). Gray bats show strong philopatry to both summering and wintering sites (Tuttle 1976; Tuttle 1979; Kennedy and Tuttle 2005; Martin 2007).

Although individuals may travel up to 35 kilometers between prime feeding areas over lakes or rivers and occupied caves (LaVal et al. 1977, Tuttle and Stevenson 1977, Tuttle and Kennedy 2005), most maternity colonies are 1-4 kilometers from foraging locations (Tuttle 1976). The home range of one colony included five caves and covered an area approximately 50 kilometers long by 5 kilometers wide (Tuttle 1976). Newly volant gray bats travel 0.0-6.6 kilometers between roost caves and foraging areas (Tuttle 1976).

Bachelor males form separate aggregations within a colony home range that usually includes several caves extending up to 70 kilometers along a particular river valley (Tuttle and Kennedy 2005).

Palustrine Habitat(s): Riparian
Subterranean Habitat(s): Subterrestrial
Habitat Comments: Roost sites are nearly exclusively restricted to caves throughout the year (Hall and Wilson 1966, Barbour and Davis 1969, Tuttle 1976), though only a few percent of available caves are suitable (Tuttle 1979). Winter roosts are in deep vertical caves with domed halls. Large summer colonies utilize caves that trap warm air and provide restricted rooms or domed ceilings; maternity caves often have a stream flowing through them and are separate from the caves used in summer by males.

Occasionally non-cave roost sites are used. Hays and Bingman (1964) reported a colony in a storm sewer in Pittsburg, Kansas and, in 1988, a maternity colony was discovered using a storm sewer in Kansas (Decher and Choate 1988). Harvey and McDaniel (1988) located a maternity colony in a storm sewer in downtown Newark, Independence County, Arkansas. There are occasional reports of mines (Sealander 1979, Thom 1981, Brack et al. 1984, Harvey 1988) and buildings (Gunier and Elder 1971) being used as roost sites.

Winter caves are deep and vertical and provide a large volume of air below the lowest entrance that acts as a cold air trap (Tuttle 1976). Cold air flows in and is trapped during successive winters, providing mean annual temperatures 6 degrees C or more below the above-ground mean annual temperature (Tuttle 1978). Hibernation sites often have multiple entrances, good air flow (Martin 2007), and temperatures of approximately 5-9 C, though 1-4 C may be preferred (Tuttle and Kennedy 2005).

In the summer, maternity colonies prefer caves that act as warm air traps or that provide restricted rooms or domed ceilings that are capable of trapping the combined body heat from thousands of clustered individuals (Tuttle 1975, Tuttle and Stevenson 1977). Cave temperatures range from 14 to 24 C. Undisturbed summer colonies may contain up to 250,000 bats, and average 10,000 to 25,000 (Tuttle 1979). Summer caves are nearly always located within 1 km of a river or reservoir over which the bats forage (Tuttle 1979).

Tuttle (1979) showed that forested areas along the banks of streams and lakes provide important protection for adults and young. Young often feed and take shelter in forest areas near the entrance to cave roosts (Tuttle 1979). Do not feed in areas along rivers or reservoirs where the forest has been cleared (LaVal et al. 1977; Tuttle and Stevenson, in prep.).

Yearlings and adult males segregate into nomadic summer colonies that tend to roost in caves within a few kilometers of ones selected by adult females (Layne 1978).

Adult Food Habits: Invertivore
Immature Food Habits: Invertivore
Food Comments: Feeds mostly upon flying insects, including mayflies (CHOROTERPES spp., STENOCRON spp.) and beetles (Tuttle et al., Lacki et al. 1995); diet may vary with local resources and habitat.

Foraging is generally parallel to streams, over the water at heights of 2 to 3 m (LaVal et al. 1977). Caire et al. (1989) stated that this bats is apparently adapted to forest foraging and rarely is collected in the open or over streams; geographic variation? The energy demands on adult females are tremendous during lactation, and individual females sometimes feed continuously for seven or more hours per night (Tuttle and Stevenson).

Adult Phenology: Hibernates/aestivates, Nocturnal
Immature Phenology: Hibernates/aestivates, Nocturnal
Phenology Comments: Females enter hibernation in fall after mating, followed by males and juveniles several weeks later (most females are hibernating by early October, most others are in hibernatation by early November) (Tuttle 1976). Adult females emerge from hibernation late March-early April. Others emerge mid-April to mid-May (Tuttle 1976). Forages at night.
Colonial Breeder: Y
Length: 10 centimeters
Weight: 9 grams
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: Land protection agreements for important caves, gating/fencing/posting of cave entrances, protection and restoration of foraging habitat, and monitoring of populations have enabled good documentation of substantial population recovery over the past several decades. Populations require regular monitoring to minimize disturbance. Species is vulnerable to difficult-to-manage harmful effects of a fungal disease (white-nose syndrome).
Restoration Potential: Cave protection has resulted in very good recovery. Some caves have had spectacular increases in gray bat populations due to proper gating and signs. In some instances, protecting caves that been abandoned has resulted in re-occupation. The ability to control factors such as water pollution, siltation, deforestation, and pesticide use will influence the ability of the gray bat to recover.
Preserve Selection & Design Considerations: Effective conservation includes adequate protection of winter roosts (hibernacula), summer maternity colonies, bachelor caves, and significant migratory (temporary) roosts. Buffer zones of forest should be maintained and forested corridors to prime forage areas over rivers and reservoirs protected. Steps should be taken to reduce pollution of waterways, siltation, or use of pesticides near caves.
Management Requirements: Major management concerns include reducing human disturbance to caves. Properly designed physical barriers are critical. Improperly constructed gates can alter the air flow, trap debris, and block the entrance by not allowing enough flight space (Brady et al. 1982). Temperature and humidity are directly related to the number of entrances to a cave. Most hibernating bats require exceptionally cold caves for hibernation and unusually warm caves for summer. Improperly constructed physical barriers can alter the exchange of air with the outside environment, which may cause significant changes in interior temperatures and humidity, causing the bats to abandon the cave (Currie, pers. comm., 1992). Improperly constructed gates may also subject the bats to severe predation as they attempt to pass through the gates (Tuttle 1977). Gray bats have accepted all properly designed gates but will not accept full gates (i.e., gates that completely fill the entrance). Wildlife managers should consult with members of the Gray Bat Recovery Team. Tuttle (1977) and Tuttle and Stevenson (1977) provided details on acceptable types of physical barriers. See also White and Seginak (1987) for information on gate design.

Public education and elimination of trails leading to cave entrances are important (Tuttle 1979, Brady et al. 1982). Signs may be appropriate at caves that are rarely visited or in conjunction with physical barriers. They should be located so that they are visible to people but do not impede flying bats or air flow. Brady et al. (1982) gave suggestions on the wording of signs. Signs may not be appropriate if they would attract people to an entrance that they otherwise would not have seen. Educating the public about the benefits of bats and communicating with local spelunkers and researchers should help reduce unintentional disturbance. Most people do not find caves if there is no trail leading to the entrance. Covering trails or preventing boat access will also reduce human disturbance.

Of importance are restoration of degraded foraging habitat and protection against environmental disturbance. Human disturbance at the cave site is a major cause of population decline (Barbour and Davis 1969, Tuttle 1979). Disturbance at maternity caves can result in thousands of flightless young being dislodged and falling to their deaths (Tuttle 1979). Caves used by nusery colonies should not be entered from late April through at least mid-July, particularly late May through early July (Brady et al. 1982); if a cave must be entered during this period, it should be restricted to a one-hour visit immediately following the evening emergence of adults (Layne 1978). Disturbance during the winter causes partial or complete arousal from hibernation. Brady et al. (1982) pointed out that a number of human disturbances during winter can exhaust the bats' limited energy reserves and result in a high mortality rate. Tuttle (in Brady et al. 1982) found that weight loss among gray bats during the first hour after arousal was 0.48 grams, compared to a normal hibernation loss of 0.01 grams per day.

At least formerly. pesticides were a major threat to the gray bat (Clark et al. 1978, 1980, 1982). At least one colony was destroyed because of pesticide poisoning (Clark 1983). Dieldrin was sprayed in corn fields to control cutworms (larvae of Noctuidae moths; Clark et al. 1978). Bats consume moths with dieldrin and juvenile gray bats receive concentrated amounts through the female's milk. The rapid fat utilization in juveniles because of the stress of flight initiation can cause fatal concentrations in brain tissues (Clark et al. 1978). Dieldrin was banned in 1974. Clark et al. (1980) documented deaths in gray bats from heptachlor residues reflecting a change by local farmers from aldrin to heptachlor as stocks of aldrin became depleted. Guano analyses can be used to identify major contaminants affecting bat populations.

Destruction of food, foraging habitats, and caves is also a management concern. Mayfly larvae are susceptible to aquatic pollution, turbidity, and siltation caused by strip mines in the watershed or farming practices (Fremling 1968, Tuttle 1979). Deforestation of the watershed reduces foraging habitat (LaVal et al. 1977, Tuttle and Stevenson in prep.). Young gray bats use the forest near the cave entrance for cover while perfecting flight abilities (Tuttle 1976). Both juveniles and adults use forested areas for protection from predators, specifically screech owls (Tuttle 1979). Impoundment of waterways has submerged important cave sites and made other caves more accessible to humans (Barbour and Davis 1969, LaVal et al. 1977, Tuttle 1979, Brady et al. 1982).

Natural calamities, such as submersion of the cave during a flood or a natural cave-in, also affect gray bat populations (Tuttle 1979). Flood frequency and magnitude can be affected by channelization and other human activities.

Monitoring Requirements: Caves used for hibernation, maternity sites, and migratory roosts should be monitored. Yearly censuses must be conducted with the least amount of disturbance to the bats. Hibernacula should not be entered from mid-August to early May, and maternity and bachelor caves should be left alone between mid-April and mid-July. Summer caves should be entered at night, after the bats emerge. The technique that causes the least disturbance is to measure the amount of reddish stains on the ceiling (some caves do not have this) and to measure the amount of bat guano (Tuttle 1979, Brady et al. 1982). New guano can be distinguished from old by characteristics such as moisture content, kinds and life stages of associated fungi and invertebrates, and the stage of decay of dead bats. To estimate the bat population, the area of the floor covered by new guano (measured in square meters) should be multiplied by the average bat clustering density (in maternity caves) of 1,828 bats/sq m and rounded to the nearest hundred. Guano measurements in some caves may be difficult because flooding or people walking through may destroy some of the guano. See Sabol and Hudson (1995) for information on a semi-automated, noninvasive technique that uses thermal infrared-imaging to estimate population size.
Management Research Needs: Research the effects of habitat disturbance, water pollution, and siltation on food sources and the effects of pesticides and deforestation on population trends.
Biological Research Needs: One of the greatest needs for this species is a quick, quiet, systematic and standardized method for conducting colony counts at hibernacula.  Due to the complexity of the caves they tend to inhabit, the challenging terrain makes surveying very slow work. Consequently, individuals, clusters and whole colonies can awaken and fly before a survey is complete ? making a census nearly impossible.  The wakening of colonies during surveys is very common and problematic for our ability to estimate colony size and trends over time. Source: K. Gillies (pers. comm., 2015).
Population/Occurrence Delineation
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Group Name: Small and Medium Bats

Use Class: Bachelor colony
Subtype(s): Diurnal Roost, Foraging Area, Nocturnal Roost
Minimum Criteria for an Occurrence: An area occupied either historically or at present by a persisting or recurring population of males during summer (approximately May through August). Includes mist net captures away from roost sites obtained during the summer months even if the actual roost site(s) are not known. Identification evidence minimally includes collection or reliable observation and detailed documentation of one or more individuals. In certain regions, recorded echolocation sequences of individuals may be considered reliable observations for certain species that can be confidently identified by their echolocation calls alone, although caution must be used in determining Location Use Class for such observations during the breeding season.
Mapping Guidance: EO includes both the colony site and the associated foraging areas. If separate, the colony site and foraging areas are bounded by separate polygons; that is, areas over which the bats simply commute to and from foraging areas and the colony are not included in the EO.
Separation Barriers: None.
Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: The assigned separation distance is intended to generate occurrences that consist of spatially proximate roost sites and capture locations. However, include in the same occurrence (1) any roost sites between which significant of individuals are known to move, regardless of how far apart they are, and (2) known significant foraging areas of occurrences that are based on roost sites.

In two studies, male MYOTIS SODALIS foraged a maximum of 2.0 and 4.2 kilometers from their summer roosts (summarized in USFWS 1999).

Date: 29Mar2004
Author: Cannings, S., and G. Hammerson

Use Class: Breeding
Minimum Criteria for an Occurrence: An area occupied either historically or at present by a persisting or recurring breeding population during spring/summer (approximately May through August). Includes mist net captures away from colony sites obtained even if the associated roost site is not known. Identification evidence minimally includes collection or reliable observation and detailed documentation of one or more individuals. In certain regions, echolocation sequences of individuals may be considered reliable observations for certain species that can be confidently identified by their echolocation calls alone, although caution must be used in determining Location Use Class for such observations during the breeding season.
Separation Barriers: None.
Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: It is impractical to attempt to delineate occurrences on the basis of discrete populations. Instead, the assigned separation distance is intended to generate occurrences that consist of spatially proximate roost sites and capture locations.
Date: 02Jul2014
Author: Hammerson, G.

Use Class: Hibernaculum
Subtype(s): Pre-hibernation roost site, Hibernaculum
Minimum Criteria for an Occurrence: A site occupied either historically or at present by a recurring population of hibernating individuals. Identification evidence minimally includes collection or reliable observation and detailed documentation of one or more individuals. EO also includes immediately surrounding areas used by bats immediately before hibernation, where these areas are known.
Mapping Guidance: Cave/mine passages should be projected to the surface for the purpose of mapping EO boundary.
Separation Barriers: None.
Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: These bats sometimes move long distances between different hibernacula. For example, individuals of M. LUCIFUGUS and M. SEPTENTRIONALIS have been recorded flying up to 219 and 89 kilometers respectively between hibernacula during the winter months (Linzey 1998, Griffin 1940). However,
such movements are not a good basis for distinguishing occurrences (occurrences would become too expansive). The assigned separation distance is intended to generate occurrences that consist of spatially proximate hibernacula.

Separation distances suggested take into account the fact that, during the fall, some bats (e.g. M. SODALIS) swarm and mate at their hibernaculum, and males roost in trees nearby during the day and fly to the cave during the night. In two studies, M. SODALIS males roosted within a maximum of 5.6 kilometers of the hibernaculum (Kiser and Elliott 1996; Craig Stihler, West Virginia Division of Natural Resources, pers. observ., October 1996, cited in USFWS 1999).

Although they do not generally fly from one hibernaculum to another, hibernating bats are known to wake and move around to some extent within their hibernating site. As long as the areas are connected (even though they may not be passable by humans) the bats could be expected to move from one part of the system to another (e.g. MYOTIS SODALIS, Clawson et al. 1980).

Date: 29Mar2004
Author: Cannings, S., and G. Hammerson

Use Class: Maternity colony
Subtype(s): Colony Site, Foraging Area, Nocturnal Roost
Minimum Criteria for an Occurrence: An area occupied either historically or at present by a persisting or recurring population of breeding females and their young during summer (approximately May through August). Includes mist net captures away from colony sites obtained during the summer months even if the associated roost site is not known. Identification evidence minimally includes collection or reliable observation and detailed documentation of one or more individuals. In certain regions, echolocation sequences of individuals may be considered reliable observations for certain species that can be confidently identified by their echolocation calls alone, although caution must be used in determining Location Use Class for such observations during the breeding season.
Mapping Guidance: The EO includes both the colony site and the associated foraging areas. If separate, the colony site and foraging areas are bounded by separate polygons; that is, areas over which the bats simply commute to and from foraging areas and the colony are not included in the EO.
Separation Barriers: None.
Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: It is impractical to attempt to delineate occurrences on the basis of discrete populations. Instead, the assigned separation distance is intended to generate occurrences that consist of spatially proximate roost sites and capture locations.

Nursing female Myotis sodalis moved an average of 1.04 kilometers from roost to center of foraging area, giving a mean foraging diameter of 2.08 kilometers; however, post-lactating females moved more than twice as far, travelling an average of 2.6 kilometers (Garner and Gardner 1992). In Indiana, 11 foraging adult females that were tracked for 2-7 days moved up to 8.4 km from their roost; home range during this brief period averaged 3.35 square kilometers (Sparks et al. 2005). Myotis grisescens females move up to 6.6 kilometers (Tuttle 1976). Female M. septentrionalis had an average foraging home range of 61.1 hectares (Menzel et al. 1999), equivalent to a circle with a diameter of 880 meters.

Date: 08Mar2001
Author: Cannings, S.

Use Class: Nonbreeding
Subtype(s): Diurnal Roost, Foraging Area, Nocturnal Roost
Minimum Criteria for an Occurrence: A site occupied either historically or at present by a recurring population of migrating or otherwise nonhibernating individuals during the nonbreeding season. Identification evidence minimally includes collection or reliable observation and detailed documentation of one or more individuals. In certain regions, recorded echolocation sequences of individuals may be considered reliable observations for certain species that can be confidently identified by their echolocation calls alone.
Separation Barriers: None.
Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: The assigned separation distance is intended to generate occurrences that consist of spatially proximate roost sites and capture locations. However, include in the same occurrence (1) any roost sites between which individuals are known to move, regardless of how far apart they are, and (2) known significant foraging areas of occurrences that are based on roost sites.

In California, Fellers and Pierson (2002) studied a group of Corynorhinus townsendii inhabiting a maternity colony site after the nursery season had passed and found that the mean center of female foraging activity was 3.2 kilometers from the diurnal roost, whereas the mean center of male foraging activity was only 1.3 kilometers from the roost. No bats traveled more than 10.5 kilometers from the roost, and individuals showed considerable loyalty to the primary roost. Otherwise, little movement data are available.

Date: 19Apr2001
Author: Cannings, S.

Use Class: Roost
Minimum Criteria for an Occurrence: An area occupied either historically or at present by a persisting or recurring population during summer  (approximately May through August). Includes counts of individuals from roost sites obtained during the summer months during pup rearing and summer residence periods. Identification evidence minimally includes collection or reliable observation and detailed documentation of one or more individuals during roost counts.
Mapping Guidance: EO includes both the colony site and an approximation of the associated foraging areas. If separate, the colony site and foraging areas are bounded by separate polygons; that is, areas over which the bats simply commute to and from foraging areas and the colony are not included in the EO.
Separation Barriers: None
Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: It is impractical to attempt to delineate occurrences on the basis of discrete populations. Instead, the assigned separation distance is intended to generate occurrences that consist of spatially proximate roost sites.
Date: 01Dec2017
Author: Staffen, R.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 21Aug2015
NatureServe Conservation Status Factors Author: Hammerson, G.
Management Information Edition Date: 08Apr1992
Management Information Edition Author: EVANS, J. E., N. DRILLING, R. L. HENSON, AND G. HAMMERSON
Element Ecology & Life History Edition Date: 05Sep1996
Element Ecology & Life History Author(s): Hammerson, G.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
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